I would agree with comments here about ALL of the technical cameras being precision systems. At the end of the day they are simple frameworks that hold the sensor and lens in the right place with various combinations of shift or tilts.

Sure Alpa make a big deal about the shimming process for precise alignment of the sensor with the camera and I can definitely state that every back that I've owned and mounted to my Alpa has needed a different shim setting, be it a Leaf Aptus, P40+, two different P25+s and my IQ160. The difference was plainly visible in images. How much of a difference does it make at focus points other than infinity? Well, not much, but what it does mean is that when I dial in 6in, 5ft or 10ft or 100ft based on a laser measurement, that's what it is. DoF will cover some of that but what I can rely on is that infinity is always sharp. Arca can do the same thing in the field with their offset adjustment factor - no difference, just an alternative means of achieving the same goal. Cambo - I believe that there are ways to achieve it too, although not per back with the same camera if you have multiple backs (that I'm aware of anyway). It is a fair point to say that the correct alignment of sensor and lenses does rely on all lenses being identically aligned accurately. Alpa do this, as I'm sure that all other vendors do too but there can be some variation in real lenses until they are all adjusted together (just like you'll find with Leica etc).

I chose Alpa because it fits my shooting needs and I like the ergonomics and aesthetics. I simply enjoy using it. I would be the first to say though that it isn't perfect, just as I would assert that neither are the Cambo or Arca 'perfect' either. They all have their own foibles that you can only really appreciate if you try them. Personally, I think that the Alpa is the weakest of the trio for tilts due to the lack of nodal tilts on lenses - I've shot with the Cambo and I personally found it easier to use with tilts (others may disagree). I haven't shot with the Arca but I've ridden along with plenty of Arca shooters and they like using that system. The Alpa and Cambo rely on real world distances scribed on a traditional helicoid focus ring - Arca take a different approach that may or may not appeal. It didn't for me but it seems to be just as effective.

What I would reiterate is that you really need to follow the advice given here by multiple posters which is to try them for a while and see what works for you. You may fall in lust with the Alpa fit, finish & feel or you may prefer the ergonomics and fit & finish of the Cambo/Arca but you certainly won't know that by just reading these threads.

If I didn't already have my two Alpas, I'd happily shoot with either the Cambo or Arca all things being equal. Is there any difference in the quality of images shot with an Alpa, Arca or Cambo? No. The difference is only in how much you enjoy using each of them and how efficient and effective you find them in real use. The glass is the same. The backs you use are the same.

Sorry for asking, but: If you had five different backs and all needed shimming does it not mean that four of the five were outside tolerance? My impression is that Phase One tolerances are 12 microns, that is 0.0012 mm, so if all your Phase backs were within tolerance you would only need to shim on one.

I would agree with comments here about ALL of the technical cameras being precision systems. At the end of the day they are simple frameworks that hold the sensor and lens in the right place with various combinations of shift or tilts.

In your article you indicate that 20x loupe is needed for exact focusing on ground glass. That makes sense to me. Does that say that ground glass with viewfinder loupe magnifying 4X is not accurate enough for correct focusing?

Just one crazy question... if it is indeed key to postion the backs relative to the lens mount with such a degree of accuracy... what are the odds that a sliding back mechanism is repeatible enough not to generate any loss of quality?

The answer is probably "close to zero".

In my view this is another reason why cylindrical stitching makes more sense, you don't affect the lens/sensor relative position when you rotate the camera on a pano head.

By the way, when I interviewed the Pentax 645D product manager a few years back, he had mentioned the accurary of sensor positioning relative to lens mount as the main reason why they had decided to go with an integrated camera.

That is said to be the reason that the Hartblei HCam has a motorized slider (not that I know how it helps).

What Bernard says make a lot of sense, but on the other hand it is possible to build things to a very high precision.

This reminds me of a story:

In the cold war Finland was neutral and was forced to buy defense equipment from both Soviet and the west. So I met this AAA (Anti Air Artillery) guy, he said that they used to have guns from Oerlikon in Switzerland and guns from Soviet. The Oerlikons were very well made and Soviet stuff also worked in the winter.

Just one crazy question... if it is indeed key to postion the backs relative to the lens mount with such a degree of accuracy... what are the odds that a sliding back mechanism is repeatible enough not to generate any loss of quality?

The answer is probably "close to zero".

In my view this is another reason why cylindrical stitching makes more sense, you don't affect the lens/sensor relative position when you rotate the camera on a pano head.

By the way, when I interviewed the Pentax 645D product manager a few years back, he had mentioned the accurary of sensor positioning relative to lens mount as the main reason why they had decided to go with an integrated camera.

Sorry for asking, but: If you had five different backs and all needed shimming does it not mean that four of the five were outside tolerance? My impression is that Phase One tolerances are 12 microns, that is 0.0012 mm, so if all your Phase backs were within tolerance you would only need to shim on one.

Another question is, how much shimming is needed to make a visible difference and at which aperture? Some authors say 0.01 mm but that does not make sense to me.

Another question. Lenses may also vary. How does Alpa adjust precision focusing scale to lens sample, do they engrave them individually or they use lenses of exactly the same focal length?

Best regardsErik

Erik

I don't follow your logic that the backs were out of spec at all. I don't recall the exact amounts but the adjustments were all very minor in each case and I have two back adapters with their own shims set now for my current P25+ & IQ160. Just watch this if you want to see this shim process in reality: http://media.luminous-landscape.com/video/misc/Alpa-Phase_Shim-1.3.mov

I believe that you would follow a similar process with an Arca to determine the offset factor for your back with the reference lens.

Regarding the lens marking, it's based on the angle of rotation of the focus ring on the helicoid. So long as infinity is known then the rest should fall in to the right place (within the tolerance of the helicoid obviously). That applies also to the HPF rings.

Sorry for asking, but: If you had five different backs and all needed shimming does it not mean that four of the five were outside tolerance? My impression is that Phase One tolerances are 12 microns, that is 0.0012 mm, so if all your Phase backs were within tolerance you would only need to shim on one.

In your article you indicate that 20x loupe is needed for exact focusing on ground glass. That makes sense to me. Does that say that ground glass with viewfinder loupe magnifying 4X is not accurate enough for correct focusing?

I feel that issue was not really addressed in the discussion so far.

What is "accurate enough" is a matter of taste.

This means that some will want Alpa shimming och Arca offset factor with their backs to get a perfect match with the precise distance scale, I'd probably calibrate the system too if I had one. The problem I have and what makes *me* defensive is when either directly or in-between the lines people say that this precision Alpa and Arca offers is *required* to make sharp images, i e that view camera and ground glass focusing is hopelessly obsolete and my Linhof Techno would be utterly useless for any serious image making. I don't agree with that, and I think the view camera has a number of strong points.

You could shim the back adapter for the sliding back if you want to, but to detect a focus shift with the ground glass which resolves about 18 megapixels the shift would have to be rather large to be detected. There's also a limit to how precise eye-hand can position the lens on the rail, which is getting within 60 um or so. So yes, the view camera although precisely manufactured and precise gears and everything the design does not allow for the same focus placement precision as Alpa or Arca RM3Di does. Is this a problem? Is it worth sacrificing the flexibility of the view camera and spending all that money on lens mounts to get the ultra-precise focus placement? I came to the conclusion "no", and I have not regretted it. But you have to be aware of the limits and adapt to it, and I can sometimes feel that there's coming a bit of FUD from the pancake camp, that all of a sudden ultra-precise focus placement has become critical to deep DoF image making.

I'm quite demanding myself though, that's why I'm using a stronger loupe than is normally sold for ground glass cameras, and I achieve higher focusing precision with that. With a 4x loupe (which is what Linhof themselves sells) the focusing precision is so poor that I'm not satisfied myself. My point is that if you give the ground glass a chance and actually try to make the best out of it, it would work for many more users than the general perception seems to be.

But as said, "accurate enough" is a matter of taste, there are for example Cambo users that focus on ground glass (rather than distance scale) with low magnification loupes and is happy with that. There is an element of skill/eyesight too, some may have very good eyes and can place precisely with a lower magnification loupe than I can. Arca recently announced an optical focusing system for their RM3Di, of course less precise than the laser distance meter method, so there are users out there that can live with "unprecise" focusing.

Just one crazy question... if it is indeed key to postion the backs relative to the lens mount with such a degree of accuracy... what are the odds that a sliding back mechanism is repeatible enough not to generate any loss of quality?

The need of that type of accuracy is over-appreciated with deep DoF image making, so don't worry. My point I'm trying to make is not that Alpa etc is *lying* about being best on precision, perhaps they are the best, the tools are indeed precise, what I mean is that there's FUD in the air indicating that those extreme amounts of precision is required to make sharp images, while I'd rather say that it's a nice to have feature that you get to pay a very large amount of money for.

In response to your question about focussing experience, the reading I had done on this topic before acquiring the IQ included the Joseph Holmes report, describing the use of a special Zeiss magnifier and the Luminous Landscape advice to use Alpas, and shim them etc. I almost lost the will to live. Actually, that is unfair, but it was all very off-putting. So I was quite surprised that, during the big camera test, my focussing efforts on the Techno proved no less accurate than they had previously been with the P45+ doing the image capture. In other words, on the captured image it is perfectly straightforward to see the zone of sharp focus, where it drops off and so on, and in most of my experiences so far it has coincided with where I thought I had focussed on. I do appreciate that any inaccuracies in the position of the focus plane can have a serious impact on image quality. I can only conclude that my Techno and sliding back (Linhof) is currently correctly zeroed and within all the necessary tolerances. I am extremely careful in focus implementation, but the last three months have taught me to feel confident that what I see on the ground glass is what I get in the file. Which is all that could be asked for really. Is 10x enough magnification? Clearly it is for me.

Some great information here.... amazing how simple discussions can change the state of your mind. Will be hunting for some local photo-outings and expeditions centering on MF... not sure there are many in Australia.Met a guy called Ken Duncan the other day, has a good website, nice guy, but people have said he's a bit commercial.

on cameras, I've now added Linhof Techno to the list. Arca is quite severely limited in terms of availability, so is looking like it will be out.So For now, it will be Alpa / Cambo / Linhof for a 3 lens kit, back, camera and bag. Thanks for all the information, I feel better prepared and more in touch with the subject. But yes, will have to handle a few machines before deciding.

My impression is that Stefan feels that Phase One stuff are quite OK regarding accuracy but he is less impressed with some of the alternatives.

If it is correct that Phase One factory tolerance is 12 microns than all phase backs out from factory should be consistent and would need no extra shimming or adjustment. The information on this seems to be contradictory. One of the posters had I think five backs and all needed different shimming.

We need to keep in mind that 12 microns is +-, so we can have a back at -12 microns and another one at +12 microns. Both would be within tolerance but the difference would be 24 microns or 0.024 mm. If we assume that largest aperture used on MF would be f/4, the resulting CoC would be 0.006mm corresponding to the pixel pitch on an IQ180, I'm pretty sure that would be visible, at least on test targets, stopping down to f/8 would reduce the CoC to 0.003 micron and that would not cause image quality reduction.

I'm no machining expert but isn't +/-12 microns quite a sloppy standard for the things we're talking about here? I've seen somewhere that at least some digital backs has internal shims, i e you can adjust the sensor position with shimming, and standard shim tape can be as thin as 5 microns, so I think it should be possible to get within +/- 5 um with relatively minor effort. I mean this is very expensive electronics so I think one should be able to demand that precision is *better* than standard products.

If I'm correctly informed the smallest step with Alpa shimming is 10 microns.

There are other sources of error though. It is beyond me why backs are not fastened with screws to the adapter plate. I got H-mount on my back and it does not exactly feel 100% tight, I haven't dared to analyze it yet but I would not be surprised if there's some +/- 10 microns in sloppy play of the fastening mechanism. Probably it's good enough, but as you never remove the back from the adapter plate I'd rather want it screwed in place. I've also been surprised of how poor quality some €500 adapter plates can be, the plate is probably very precisely machined but not seldom the attachment mechanism (H-mount, V-mount etc) which is screwed onto the plate made with a lesser standard. In one case I had to file down the screws because they were too long!

Adapter plate fastening into the tech camera is often of dove-tail type with pressure on it and has therefore probably less of a precision issue. I've noted though that typical high precision surface points in a camera are naked metal, but adapter plates are generally all black. I wonder if coloring the metal affects the thickness?

My impression is that Stefan feels that Phase One stuff are quite OK regarding accuracy but he is less impressed with some of the alternatives.

If it is correct that Phase One factory tolerance is 12 microns than all phase backs out from factory should be consistent and would need no extra shimming or adjustment. The information on this seems to be contradictory. One of the posters had I think five backs and all needed different shimming.

We need to keep in mind that 12 microns is +-, so we can have a back at -12 microns and another one at +12 microns. Both would be within tolerance but the difference would be 24 microns or 0.024 mm. If we assume that largest aperture used on MF would be f/4, the resulting CoC would be 0.006mm corresponding to the pixel pitch on an IQ180, I'm pretty sure that would be visible, at least on test targets, stopping down to f/8 would reduce the CoC to 0.003 micron and that would not cause image quality reduction.

Good points. If you wiggle the digital back on the adapter plates (especially stitching backs), there is a lot of little movement points. Also saw a Mamiya back on a Cambo with a fair amount of wiggle room. That said, it seems that the digital back takes a set on the stitching backs and seems to work well. Again, like others, shooting at f11 or f16, this hasn't seemed to matter - corner to corner are sharp. But if one were to shoot close up and wide open, these things might well add up.

The black coating is anodizing on the alum, typically chosen because of its negligible impact on alum dimensioning (architectural use). If we are in the realm of microns... perhaps it might matter.

One could see it another way: if there is really a need for super-precise focusing, then one should look for the most direct mech'l connection of lens to the back, with the fewest number of pieces and variables.

However, once the back is aligned and spaced correctly on the camera, then for most work DOF is your friend, and takes care of most other issues, much as it did in the days of film.

So I've read and re-read the post and it looks like I will be going with Cambo WRS. Few points: Ken: brilliant sense of humour. I wish I could write like that. Don: Thanks for the informative and thoughtful insight into the selection process.Torger: great review and thanks for the guidance. Again, all others and everyone, thanks for the insight. I see nothing wrong in holding and voicing our opinions and nothing wrong with marketing. Some people jumped at the suggestion that Alpa shouts "precision". In general, a few dealers I spoke to have confirmed this: somehow, people think that Alpa is precise, although thats only because no one else blows their trumpet. I think everyone should. A good friend once said: If you don't blow your trumpet, others will use it as a spitoon ( he likely borrowed it from somewhere ). It will be another 3 months until I garner enough dough to jump the ship to MF. Currently will be selling all my Leica stuff to harness the funds. Will try and post some first attempts soon.Great forum, great website. Keep it up (literally). Saty

1.: Everbody should read Joseph Holmes article, it is very informative ! There is another one from Roger Cicala - very VERY interesting thoughts and informations:http://www.canonrumors.com/tech-articles/this-lens-is-soft-and-other-myths/2.: While arguing, the accuracy of Phase and Leaf Backs are certainly on par with Hasselblad, I really don´t know if the "calibrated approach of the pairedH Bodies and Backs does really do an advantage.3.: The problem is these Hook mechanisms, they simply wear out ! The construction of these was originally done for film accuracy and although this is now longgone and over, NONE of the makers have the guts to introduce a new digitally improved mounting (Maybe even ISO standardized- hey guys sit down and talk !!!)mount that will a) keep a more simple but enduring lock and tight fit and b) is compatible between all camera systems.4.: A system with several tolerances on several planes adds these faults. trying to eliminate them with another measurement is contraproductive.This is a paradigm from system analysis - the systemical noise cannot be reduced by inducing more noise !5.:The only way to beat that mechanical "noise" added, is to use an independent control mechanism: Life View or an electronic viewfinder taking the actual chip based infos.